The present invention relates to a composition for forming an insulating film and a method for fabricating a semiconductor device, more specifically, a method for fabricating a semiconductor device including a porous insulating film, and a composition for forming a porous insulating film.
As the integration and the density of semiconductor integrated circuits are increased, the semiconductor devices are required to have more multi-level structures. On the other hand, with the increasing integration, the interconnection pitch becomes smaller, and the interconnection delay due to increased capacitances between the interconnections is a problem.
An interconnection delay is influenced by an interconnection resistance and a capacitance between interconnections. The interconnection delay is expressed byT∝CR.when the interconnection resistance is expressed by R and the capacitance between interconnections is expressed by C. In this expression, when an interconnection pitch is d, an electrode area (an area of the side surfaces of the opposed interconnections) is S, a dielectric constant ∈r, a vacuum dielectric constant is ∈o, a capacitance C between the interconnections is expressed byC=∈o∈rS/d. Accordingly, to decrease the interconnection delay it is effective means to lower the dielectric constant of the insulating film.
Conventionally, as insulating materials, inorganic films as of silicon dioxide (SiO2), silicon nitride (SiN), phospho-silicate glass (PSG), etc., and organic polymers, such as polyimide, etc., have been used. However, the dielectric constant of the CVD-SiO2 film, which is most used in the semiconductor devices is about 4. SiOF film, which is being studied as a low dielectric constant CVD film, has a dielectric constant of about 3.3-3.5 but is so hygroscopic that it absorbs humidity to increase the dielectric constant.
Recently, porous insulating film is noted as an insulating material of further lower dielectric constant. The porous insulating film is made porous by adding organic resin, etc. which are evaporated or decomposed to a material for forming a film having a low dielectric constant, and evaporating or decomposing the organic resin by heat for forming the film.
The related arts are disclosed in, e.g., Reference 1 (Japanese published unexamined patent application No. 2000-340557) and Reference 2 (Japanese published unexamined patent application No. 2004-247695).
However, the porous insulating film presently has a pore size as large as not less than 10 nm, and when the pores are increased so as to decrease the dielectric constant, the dielectric constant increase and the film strength decrease take place due to the humidity absorption. Resultantly, cracks are often formed in the insulating film, and the insulating film is often broken in bonding.